Failed to add Zoho to Gmail

Failed to add Zoho to Gmail

Hello,

I am trying to add the option to send Zoho emails via SMTP on Gmail for one of my employee, here's what I get:

Your other email provider is responding too slowly. Please try again later, or contact the administrator of your domain for further information.

Also, on my other account that I set up on my Gmail I receive emails with delay.

What is the problem?

Thanks